A vehicle may contain automatic safety restraint actuators that are activated responsive to a vehicle crash for purposes of mitigating occupant injury. Examples of such automatic safety restraint actuators include air bags, seat belt pretensioners, and deployable knee bolsters. One objective of an automatic restraint system is to mitigate occupant injury, thereby not causing more injury with the automatic restraint system than would be caused by the crash had the automatic restraint system not been activated. Generally, it is desirable to only activate automatic safety restraint actuators when needed to mitigate injury because of the expense of replacing the associated components of the safety restraint system, and because of the potential for such activations to harm occupants. This is particularly true of air bag restraint systems, wherein occupants too close to the air bag at the time of deployment--i.e. out-of-position occupants--are vulnerable to injury or death from the deploying air bag even when the associated vehicle crash is relatively mild. For example, unbelted occupants subjected to severe pre-impact braking are particularly vulnerable to being out-of-position at the time of deployment. Moreover, occupants who are of small stature or with weak constitution, such as children, small adults or people with frail bones are particularly vulnerable to injury induced by the air bag inflator. Furthermore, infants properly secured in a normally positioned rear facing infant seat (RFIS) in proximity to a front seat passenger-side air bag are also vulnerable to injury or death from the deploying air bag because of the close proximity of the infant seat's rear surface to the air bag inflator module.
Air bags can be beneficial to any forward facing occupant when that occupant is a significant distance from the inflator door. Air bags, however, can be lethal to infants in rear facing infant seats (RFIS). Air bags can also be hazardous to forward facing occupants if they are too close to the inflator at the time of vehicle impact, such as when an unbelted occupant is subjected to severe pre-impact breaking. Air bag inflators are designed with a given restraint capacity, as for example, the capacity to protect an unbelted normally seated fiftieth percentile occupant when subjected to a 30 MPH barrier equivalent crash, which results in associated energy and power levels which can be injurious to out-of-position occupants; to small or frail occupants such as children, small women, or elderly occupants; or to infants in rear facing infant seats (RFIS). While relatively infrequent, cases of injury or death caused by air bag inflators in crashes for which the occupants would have otherwise survived relatively unharmed have provided the impetus to reduce or eliminate the potential for air bag inflators to injure the occupants which they are intended to protect.
Automotive manufacturers and NHTSA are searching for methods to disable air bags in situations where they may cause more harm than good. Airbags have been developed to open with enough force to restrain a 175 lb. adult in a high velocity crash. When these air bags are deployed on children in the front passenger seat of a vehicle, they may cause serious injuries. Another potentially harmful situation is when the occupant is very close to the air bag inflator module at the time of air bag deployment. Recent NHTSA data suggests that severe injuries due to this close proximity with the inflator can be reduced or eliminated if the air bag is disabled when the occupant is closer than approximately four to ten inches from the inflator door. The region proximate to air bag inflator where the occupant could be at risk of injury from the air bag is called the "at-risk" zone. The size of the at-risk zone is dependent upon the inflation characteristics of the associated air bag inflator and the velocity of the occupant with respect to the air bag module. Previous studies had suggested that the at-risk zone extended about eight inches from the inflator door.
One technique for mitigating injury to occupants by the air bag inflator is to reduce the power and energy levels of the associated air bag inflator, for example by reducing the amount of gas generant in the air bag inflator, or the inflation rate thereof. This reduces the risk of harm to occupants by the air bag inflator while simultaneously reducing the restraint capacity of the air bag inflator, which places occupants at greater risk for injury when exposed to higher severity crashes.
Another technique for mitigating injury to occupants by the air bag inflator is to control the rate of inflation rate or the capacity of the inflator responsive to a measure of the severity of the crash. The prior art teaches the use of multi-stage inflators having distinct independent compartmentalized stages and corresponding firing circuits, whereby the stages may be fired in delayed succession to control the effective inflation rate, or stages may be inhibited from firing to control the effective inflator capacity. The prior art also teaches the use of a hybrid inflator having a combination of stored gas and plural pyrotechnic gas generator elements which are independently fired. Furthermore, the prior art also teaches the use of control valves for controlling the gaseous discharge flow from the inflator. The inflation rate and capacity may be controlled responsive to the sensed or estimated severity of the crash, whereby a low severity would require a lower inflation rate or inflation capacity than a high severity crash. Since lower severity crashes are more likely than those of higher severity, and since such a controlled inflator would likely be less aggressive under lower severity crash conditions than those of higher severity, occupants at risk of injury by the air bag inflator because of their size or position will be less likely to be injured overall because they are more likely to be exposed to a less aggressive inflator. However, the risk of injury to such occupants would not be mitigated under the conditions of higher crash severity when the inflator is intentionally made aggressive in order to provide sufficient restraint for normally positioned occupants.
Yet another technique for mitigating injury to occupants by the air bag inflator is to control the activation of the inflator responsive to the presence and position of the occupant, thereby activating the inflator only when an occupant is positioned outside the associated at-risk zone of the inflator. Recent NHTSA data suggests that severe injuries due to close proximity with the inflator can be reduced or eliminated if the air bag is disabled when the occupant is closer than approximately 4 to 10 inches from the inflator door. Such a system for disabling the air bag inflator requires a occupant sensor that is sufficiently sensitive and robust to make such a determination, while not causing the air bag inflator to be disabled when otherwise required for providing occupant restraint.
Except for some cases of oblique or side-impact crashes, it is generally desirable to not activate an automatic safety restraint actuator if an associated occupant is not present because of the otherwise unnecessary costs and inconveniences associated with the replacement of a deployed air bag inflation system. The prior art teaches various means for detecting the presence of an occupant, or the recognition of an inanimate object in the passenger-seat of a vehicle for purposes of implementing such a system. For example, weight sensors can incorporated into the seat to detect the presence of an occupant.
Yet another technique for mitigating injury to occupants by the air bag inflator is to control the inflation rate or inflation capacity of the air bag inflator responsive to presence and position of an occupant. Such a control system would most preferentially be used in conjunction with a controllable inflation system responsive to crash severity, such as described above, wherein the occupant position inputs can be used to override otherwise overly aggressive air bag inflator controls which might otherwise be indicated by the particular crash severity level but which could be injurious to occupants of small stature or weight, or to infants in rear facing infant seats. Such a system for controlling the air bag inflator requires an occupant position sensor that is robust and sufficiently accurate, and that can distinguish and discriminate various occupant seating configurations and conditions.
The prior art teaches the use of sensors incorporated into the seat to detect the presence, weight, or seating position of the occupant. U.S. Pat. Nos. 3,672,699, 3,767,002, 5,161,820, 5,474,327, and 5,612,876 teach the use of occupant presence sensors incorporated into the seat to control the activation of the associated air bag inflator. U.S. Pat. No. 5,205,582 teaches a system for which the air bag inflator associated with an unoccupied seat is activated for accelerations above a second crash deceleration threshold, and otherwise deactivated. U.S. Pat. No. 5,074,583 teaches a plurality of sensors incorporated into the seat to detect occupant weight and seating position for purposes of controlling an air bag system. U.S. Pat. Nos. 5,232,243, 5,494,311, and 5,624,132 teaches an array of force sensing film elements incorporated into the seat for purposes of detecting the presence, weight, or position of an occupant for controlling either a multi-stage air bag inflator, an inflator vent valve, or the spatial orientation of the air bag inflator. U.S. Pat. No. 5,404,128 teaches the use of a vibration sensor incorporated into the seat to detect the subtle vibrations caused by the breathing and heart rhythms so as to determine whether or not a person is present. U.S. Pat. No. 5,573,269 teaches a means for correcting a seat weight measurement using seat back inclination angle and foot location. For some systems which incorporate seat weight as means for controlling the activation of an air bag inflator, the air bag inflator is required to be disabled if the sensed occupant weight is less than 30 Kg in order to assure that the air bag inflator is enabled for a fifth percentile female, but disabled for an infant in a rear facing infant seat. In some cases, as for example when the seat belt securing the infant seat is pulled too tight, an associated seat weight sensor could sense an apparent weight greater than the associated cut-off threshold so as to incorrectly enable the air bag inflator when a rear facing infant seat is present.
U.S. Pat. Nos. 5,071,160 and 5,118,134 teach the combination of sensing occupant position and/or velocity, and vehicle acceleration for purposes of controlling an inflator. Both of these patents teach by example the use of ultrasonic ranging to sense occupant position. U.S. Pat. No. 5,071,160 also teaches by example the use of a passive infrared occupant position sensor, while U.S. Pat. No. 5,118,134 teaches the use of a microwave sensor. U.S. Pat. No. 5,398,185 teaches the use of a plurality of occupant position sensors in a system for controlling safety restraint actuators in response thereto.
The prior art teaches the use of one or more ultrasonic beams reflected off the surface of an object to sense the location of the surface of the object. U.S. Pat. No. 5,330,226 teaches the combination of an ultrasonic ranging sensor mounted in the instrument panel and an overhead passive infrared sensor to sense occupant position for controlling a multi-stage air bag inflator or a vent valve connected thereto. U.S. Pat. Nos. 5,413,378, 5,439,249, and 5,626,359 teach the combination of ultrasonic sensors mounted in the dash and seat in combination with other seat sensors to detect the position and weight of the occupant for purposes of controlling an air bag inflator module. U.S. Pat. No. 5,482,314 teaches the combination of ultrasonic and passive infrared sensors together with associated signal processing for purposes of determining whether or not to deactivate a passive restraint system. U.S. Pat. Nos. 5,653,462 and 5,829,782 teach system for identifying and monitoring the contents of a passenger compartment by illuminating an object with a wave generator that directs waves towards the vehicle seat, and processing the received signal with a neural network or other pattern recognition system. Furthermore, U.S. Pat. No. 5,653,462 illustrates a system wherein the wave signal is first reflected off the windshield before reaching the vehicle seat.
The prior art also teaches the use of infrared beams reflected off the surface of an object to sense the location of the surface of the object. U.S. Pat. Nos. 5,446,661, and 5,490,069 teach an infrared beam directed by a transmitter at a point of reflection on the object. A receiver detects the radiation scattered from the point of reflection, and measures the distance of the point of reflection from the transmitter based upon a triangulation of the transmitted and received beams for purposes of controlling the activation of a safety restraint system. These patents also teach the combination of an infrared beam occupant position sensor with an acceleration sensor for purposes of controlling an air bag inflation system. U.S. Pat. No. 5,549,323 teaches the incorporation of a light beam occupant sensor into an air bag door. Furthermore, infrared beam sensors are commonly used as range-finders in automatic focusing cameras.
The prior art of U.S. Pat. Nos. 4,625,329, 5,528,698, and 5,531,472 teach the use of imaging systems to detect occupant position, the later two of which use this information for purposes of controlling an air bag inflator. U.S. Pat. Nos. 5,528,698, 5,454,591, 5,515,933, 5,570,903, and 5,618,056 teach various means of detecting the presence of a rear facing infant seat for purposes of disabling an associated air bag inflator.
The prior art also teaches the use of capacitive sensing to detect the presence, proximity, or position of an occupant. U.S. Pat. No. 3,740,567 teaches the use of electrodes incorporated into the base and back of the seat respectively, together with a capacitance responsive circuit, for purposes of discriminating between human occupants and animals or packages resting on an automobile seat. U.S. Pat. No. 3,898,472 teaches an occupant detection apparatus which includes a metallic electrode which is disposed to cooperate with the body of an automobile to form an occupant sensing capacitor, together with related circuitry which senses variations in the associated capacitance responsive to the presence of an occupant. U.S. Pat. No. 4,300,116 teaches the use of a capacitive sensor to detect people proximate the exterior of a vehicle. U.S. Pat. No. 4,796,013 teaches a capacitive occupancy detector wherein the capacitance is sensed between the base of the seat and the roof of the vehicle. U.S. Pat. No. 4,831,279 teaches a capacity responsive control circuit for detecting transient capacitive changes related to the presence of a person. U.S. Pat. Nos. 4,980,519 and 5,214,388 teach the use of an array of capacitive sensors for detecting the proximity of an object. U.S. Pat. No. 5,247,261 teaches the use of an electric field responsive sensor to measure the position of a point with respect to at least one axis. U.S. Pat. No. 5,411,289 teaches the use of a capacitive sensor incorporated into the back rest of the seat to detect occupant presence. U.S. Pat. No. 5,525,843 teaches the use of electrodes incorporated into the base and back of the seat for purpose of detecting the presence of an occupant, whereby the electrodes are substantially insulated from the vehicle chassis when the detection circuit is active. U.S. Pat. No. 5,602,734 teaches an array of electrodes mounted above the occupant for purposes of sensing occupant position based upon the influence of the occupant on the capacitance amongst the electrodes.
The prior art teaches systems--used alone or in combination--for suppressing the passenger air bag in dangerous situations. These systems incorporate various sensing technologies, for example:
Active infra-red sensors
Passive infra-red sensors (heat detectors)
Ultrasonic sensors
Capacitive sensors
Weight sensors (including various sensor technologies and measurement methods)
Child seat "tag" sensors
Vision-based systems
An objective of these sensors is to determine when an occupant is very close to the inflator door and in the path of the deploying air bag, particularly out-of-position occupants and rear facing infants. Once detected, these systems need to employ the correct airbag deployment strategy such that the passenger side airbag is disabled when a rear facing infant seat is present, or when a person is within a specified region near the inflator door at the time a crash occurs. A complicating situation for the sensor is when there is an object, but no part of the occupant in the at-risk zone. Usually the air bag could still be beneficial for the occupant, especially if the object in the at-risk zone is a low density or low mass object like a newspaper or a map. Systems that only use ultrasonic and optical sensing mechanisms can be blocked by newspapers. Ultrasonic sensors in some configurations will be affected by environmental conditions (temperature, humidity, altitude) because the speed of sound changes depending on the environment. Any sensing system that needs a clear line of sight between the sensor and the occupant requires the sensor to be visible to the occupant.
Radar systems can be used to measure the range to an object; however, there is a perception that biological tissue may be adversely affected by the continuous exposure thereof to a radar beam.
Usually two or more of these sensors are used together in an attempt to identify child seats, small occupants, empty seats, large occupants and out-of-position occupants. The more sensors that are used, the better the chance for a high performance system. The costs of systems that use many sensors however, can become prohibitively high because of the large number of components and the increased assembly complexity of the vehicle.
Sensors which measure the distance between a point of reference and the surface of an object, such as ultrasonic or infrared beam sensors, are also vulnerable to false measurements, as would be caused for example by the presence of the extremities of an occupant, or by the presence of an object such as a scarf or newspaper held thereby, in proximity to the sensor. These types of sensors could be used to monitor the at-risk zone proximate the inflator door, but are subject to several disadvantages. In particular, infrared based systems usually incorporate a beam much narrower than the volume of the at-risk zone such that multiple beams may be required to reliably sense an object anywhere inside the at-risk zone. The incorporation of multiple beams results in extra cost, complexity, and potentially slowed response. Furthermore, both infrared beam and ultrasonic base sensors would require a significant amount of hardware proximate the inflator door if the at-risk zone proximate the inflator is to be monitored.
One disadvantage of many occupant detection systems is that they do not gather the most relevant information to determine if the occupant is in an at-risk zone around the inflator module. Occupant detection systems that are mounted above the passenger and look down on the seat area have the wrong physical perspective to directly monitor the region around the inflator door. Even if an ideal set of roof mounted sensors can reliably determine the occupant's gross position--which is a very challenging task,--the actual volume between the inflator door and the occupant may be blocked to the sensors by the occupant's body. If the criteria for controlling the activation of an air bag inflator were in part based on the proximity of the occupant's body to the air bag inflator door, then overhead sensors simply cannot reliably obtain the relevant information. Systems that only use ultrasonic and optical sensing mechanisms can be blocked by newspapers. Ultrasonic sensors in some configurations will be affected by environmental conditions (temperature, humidity, altitude) because the speed of sound changes depending on the environment. Any sensing system that needs a clear line of sight between the sensor and the occupant requires the sensor to be visible to the occupant.
Some prior-art occupant detection systems attempt to identify the type of occupant or object in the passenger side seat, for example to discriminate a rear facing infant seat from a normally seated adult in the passenger seat. However, this is generally a very challenging task as there are a large variety of possible situations. Sensor systems that depend upon distance measurements to identify occupant situations generally use information from a relatively small number of points in space for identifying the particular type of occupant in the seat from amongst many possibilities. Results from these systems can be unreliable because a particular situation can be significantly changed by simple and common acts such as tossing a blanket over the occupant. Systems than can distinguish the occupant situation may be limited by the inability to disable the air bag during a pre-impact breaking event. Moreover, the algorithms used in those systems are sometimes so complex that performance is sometimes unpredictable. While complex algorithms can sometimes makeup for the lack of direct sensory information, the same algorithms can sometimes create performance anomalies.